Area of the Art
The invention relates generally to optical blood hemostatic analysis methods and specifically to methods for quantitatively measuring the concentration of soluble fibrin molecules in opaque body fluids such as whole blood.
Soluble fibrin (SF) molecules are generated from fibrinogen molecules when thrombin cleaves the alpha and beta polypeptide chains of the fibrinogen molecules. The presence of SF molecules in the blood stream is one of the most sensitive indicators of early disseminated intravascular clotting (DIC). DIC poses a great threat to patients during major surgery and after severe trauma. Therefore, a technique for rapidly and quantitatively measuring levels of soluble fibrin in whole blood would be very useful during major surgery and after severe trauma.
Although the measurement of SF has been carried out for many years, the measurement of soluble fibrin under the circumstances of major surgery or severe trauma has always been problematic and the technique is seldomly used. All available techniques for SF measurement require that the procedure be run on plasma rather than on whole blood; such a procedure takes additional time. In addition, most available techniques are only semiquantitative (the results are in the form of (+ xe2x80x94 ++++)). These problems have prevented the test from being widely used. Available techniques must utilize plasma because the detection of SF precipitates is done optically and a clear fluid medium is thus a necessity. In addition, in those techniques, optical endpoints are desirable for tests of the coagulation process as they typically permit the entire reaction chamber to be disposable. Optical endpoints for SF in whole blood are typically useless, however, owing to the opacity of the whole blood and the widely distributed nature of the SF precipitates. Therefore, the previous techniques that utilize optical endpoints require the use of plasma.
Plasma is prepared from whole blood by centrifugation. The centrifugation step typically requires the sample to be transported out of the operating room to an analytical laboratory. The minimum time for a test result thus becomes 30-45 minutes. Once the transport time has been added to the time required for centrifugation and the time for analysis, the test result is useless in the context of the operating room as the patient""s condition would have likely changed substantially in the meantime. For studying the kinetics of SF conducting a test that requires preparation of plasma is likewise problematic as the reaction of thrombin on fibrinogen takes place on the order of seconds and cannot be stopped without using anti-polymerizing agents that interfere with subsequent detection of SF.
Most available methods for detection of SF quantify the amount of SF present only in a very approximate manner as in + xe2x80x94 ++++. Those that do a more rigorous quantification require additional steps such as:
1. removing the SF precipitates, drying and weighing the precipitates;
2. removing the SF precipitates, analyzing them for protein content;
3. Immunologically precipitating the SF precipitates, using a second antibody to quantify the amount.
All of these techniques add even more time to the SF analysis. They render the test less useful as a result.
Therefore, a need exists to develop a method that performs a SF test in an opaque suspension such as whole blood. Such a method would have far greater utility than presently available tests which, due to their optical endpoints, must be performed in plasma. Indeed, it is only whole blood tests that can be utilized in an operating room where the rapid measurement of SF will permit the surgeon or the anesthesiologist to take immediate steps to correct the conditions that are leading towards DIC.
It is an object of the present invention to provide a method for rapidly quantifying soluble fibrin optically in opaque suspensions of whole blood so as to render the test useful in the operating room under conditions of major surgery and in the presence of severe trauma where DIC is likely to supervene.
These objectives and advantages are achieved by a method of the present invention. In accordance with the embodiments of the present invention, the method includes the steps of:
(a) mixing a portion of the opaque specimen fluid in a transparent container with a sufficient amount of precipitating reagent under a condition that causes the soluble fibrin to precipitate;
(b) aggregating and concentrating the soluble fibrin precipitates in a region of the container for rendering the precipitates optically detectable in the opaque specimen fluid;
(c) optically detecting the precipitates;
(d) recording the time when the precipitates are first become optically detectable in the opaque specimen fluid, wherein the time elapsed from the addition of the precipitating reagent to the detection of the aggregated precipitates is an inverse measure of the quantity of soluble fibrin present in the opaque specimen fluid.
A method in accordance with the present invention provides a number of advantages. As explained in greater detail below, the methods of the present invention provide a rapid and quantitative measurement of soluble fibrin in opaque body fluids such as, but not limited to, whole blood. Particularly, methods of the present invention make it possible to use optical endpoints to measure SF in whole blood. It is known in the art that optical endpoints are desirable for tests of the coagulation process as they typically permit the entire reaction chamber to be disposable. However, prior to the present invention, optical endpoints for SF in whole blood are typically useless owing to the opacity of the whole blood and the widely distributed nature of the SF precipitates. The present invention allows SF to form precipitates and to be collected in a small, predictable portion of the reaction mixture so that they can be readily detected optically. When collected in high concentration, SF precipitates exclude the opaque whole blood medium and become optically detectable from outside the reaction chamber. Methods of the present invention eliminate the plasma preparation steps, and provide rapid and effective SF measurements that are readily usable in the operating room under conditions of major surgery and in the presence of severe trauma where DIC is likely to supervene. Since the present invention can accurately detect and measure the amount of soluble fibrin in an opaque specimen fluid, the present invention provides an effective means to detect early disseminated intravascular clotting.
The methods of the present invention are well suited for use during major surgery, after severe trauma, and similar circumstances where disseminated intravascular clotting poses its greatest threat. A method in accordance with the present invention can effectively detect DIC by rapidly and quantitatively measuring the soluble fibrin.
The invention is defined in its fullest scope in the appended claims and is described below in its preferred embodiments.